Dutch prosecutors say an international joint probe into the downing of Flight MH17 over eastern Ukraine is "at a very advanced stage" and that the investigators will present their first results "after this summer."

That part of the investigation, which was initially due to be concluded before the second half of the year, concerns "the weapon which was used to shoot down" the Malaysia Airlines plane and "the exact launch site of the weapon."

The airliner crashed in territory held by Russia-backed separatists on July 17, 2014, killing all 298 people onboard. Two thirds of them were Dutch.

The Dutch Safety Board concluded last year that the plane, flying from Amsterdam to Kuala Lumpur, was shot down by a Russian-made surface-to-air Buk missile.

In a June 3 statement, the Dutch Public Prosecutor's Office said the joint investigation team is "still waiting for information from the Russian Federation about Buk installations."

It said the investigators won't publish their results in a report, but will eventually include them "in a criminal file, which is intended for the hearing of the case in a court or a tribunal."

The investigators are from the Netherlands, Australia, Malaysia, Belgium, and Ukraine. Their governments have pledged to bring those responsible for the crash to justice.